The Facts:
Abbreviation - WSG
10 v 10 - 2 parties
Horde entrance - The Barrens, due North of the Crossroads, at the Ashenvale/Barrens Border.

The Basics:
WSG is a capture the flag based BG. One player clicks on the opposing team's flag back at their base and gains a very visible buff which gives him the flag (in this case the Alliance's Silverwing Flag). He then proceeds to run all the way back across the battlefield to his own teams base with the flag. If he dies on the way, the flag drops onto the ground, and a click by a team member will allow that team member to get the flag and continue running. On the other hand, if an opposing team member clicks on it the flag will be teleported back to the base from which it came. To score a point, the flag runner (person carrying the flag) must safely ferry the flag to his own base without getting killed and run to the flag spawn point. If your team's flag is there, the two flags will automatically disappear and your team will get one point, thus capturing the flag. If your team's flag is being carried by a person of the opposing team, you cannot capture the flag. You cannot pick up your own team's flag (the Horde's Warsong Flag).

The Terminology:It's fine for a new player to be confused by these truncated terms, but as you play your first five to ten WSGs you'll get the hang of it.
Offense: the offense team (Abbv - O)
Defence: the defence team (Abbv - D)
Tunnel: the tunnel which connects the base to the midfield (Abbv - tun/tunn)
Ramp: the ramp which connects the base to the midfield, going above the tunnel (no abbv)
Graveyard: the graveyard just outside the base which you respawn at (Abbv - GY)
Roof: the roof of the base, accessed by a path from the tunnel (no abbv)
Midfield: the center of the map, a big open area (Abbv - mid)
Flag Runner: the person carrying the flag (Abbv - Flag Carrier/FC/FR[sometimes confused with flag room])

The Strategy
Getting the flag: Soloist
This means one person (usually a rogue or druid with stealth) sneaking into the opponent's base and grabbing the flag, ignoring the defenders (or killing a lone defender), and rushing out through the tunnel, ramp, or GY back to base. This is good only for teams who effectively control the midfield, because the run back to base is nearly always hampered by the Allies. Most soloists run into up to five enemies in the midfield, and will require the assistance of the rest of the O team to get through. However, solo attempts are usually unsucessful because a lone person who is concentrating on running and not attacking will usually not survive the onslaught of even one or two determined Allys. If you think you stand a chance of making it, however, blow your instant or fast cast skills; mages, frost nova and blink; druids, shapeshift, nature's grasp and entangling roots; rogues, sprint; shamans, drop earthbind and frost shock; warlocks, fear attacks away; priests, psychic scream; warriors, intercept to boost speed; paladins, blessing of freedom. Use your Insignia of the Horde if you have it. However, its hard to cast and run concurrently, which makes solo attempts fail most of the time.

Getting the flag: Three to five
With 3 - 5 people all going into the Ally base together, the chances of survival are much higher. The team should engage the D, and one person should grab the flag and run out the way that the team came. The team will then fall back after or with the FC. This way, the FC will have a strong support, healing, and defence, and chances of sucess are greatly increased. An ideal O team in my opinion would be: Feral Druid, Mage, Priest (and extras for DPS and assorted skills). The druid grabs the flag and shifts into Bear form, and goes out the ramp way. Mage frost novas, and priest heals. If the defence persists after the druid, the priest can psychic scream and the mage can nova again. This should buy enough time for the FC to run to the outside area, pop a Rejuvination, shift into Travel form, and run off. The priest provides adequate healing and shielding, and the mage can use frost attacks to slow enemies. Of course, any other classes are greatly welcome too; shamans can drop earthbind after a frost nova, rogues can stunlock and give good damage, paladins can stun, heal, and give blessing of freedom. However, this may also fail without good midfield support, for 3 or 5 against the whole Ally team spells doom should they manage to concentrate on the FC.

Getting the flag: Six to eight
With 6 - 8 all going into the Ally base together and going out together, the FC is pretty safe. This bunch can probably DPS the D away in a matter of seconds, then grab the flag and go. However, this leaves nearly only 2-4 on D, and these can easily be overcome of the Allies decide to employ the same 6 - 8 tactic. If both sides grab the flags and run, it turns into a massive melee in the midfield. Then if both FCs survive, it turns into a turtle.

Defending the flag: Horde flag in spawn spot
2 - 5 should always be on D, to prevent stealthers coming in and sneaking the flag away. My idea form of D would be: Shaman, Rogue/Druid, Hunter. The shaman must plant his four totems (less if in lower level BGs) right in front of the flag spot, and replenish them when they disappear. Water and air can be anything the shaman likes, but the earth totem MUST be Earthbind, and the fire totem can either be Fire Nova, Magma, or Searing (totems can detect stealthers). Rogues and druids should always be in stealth, to dish out a stun move (Pounce/Cheap Shot), then try to stunlock the FC instead of dealing super-damage moves (Kidney Shot/Blind/Gouge/Maim as opposed to Eviscerate/Expose Armor). The hunter should lay down either Frost Trap or Freezing Trap, and spam Concussive Shot. His pet should use any stunning moves (Intimidation) or just harry the FC. The shaman should spam Frost Shock, and drop an Earthbind everytime the FC moves out of range. Everyone should also be doing damage. Warriors and paladins should also use their stunning and slowing moves (Intercept/Hammer of Justice/Hamstring). A warlock is also handy, because his curses and DoTs can kill the opponent even if he manages to evade the slowing moves.

Defending the flag: Someone carrying the Alliance flag
The FC usually camps in one of three places; the balcony, the little room on the ground floor, or the roof. He will put his back facing the wall to avoid nasty rogue/druid Ambush/Ravage damage. This also makes the flag less visible. A hunter or druid should have track humanoids on (and sometimes switch to track beasts to make sure shamans and druids are also accounted for) and warn the D of incoming O. The only difference between defending a FC and defending the base is that a healer is usually needed. Paladins, shamans, and druids can all provide healing, but I think the best is a priest, who has a powerful stamina buff, shields, a healing over time, and powerful heals.

Turtling
Turtles are situations when ALL or nearly all (8-10) of the team cram into their own flag room and go on D. This is a very, very safe way of assuring that the flag isn't taken, but it drags the game into one of attrition, and usually only ends when one team quits. 8 - 10 players can easily repel any strike force, except if all 10 of their team come, leaving the base with no D at all, which is a suicidal win-or-die manuver. There's no real strategy to breaking a turtle, at least not when the FC has a good healer supporting him.